Map constructors and operators are used to construct new map data types. OceanBase Database currently supports the map() constructor and the {} operator.
map
The map() function is used to construct a map data type. The syntax is as follows:
map(key1, value1, key2, value2, ..., keyN, valueN)
The input parameters are described as follows:
- The number of input parameters must be even. Parameters with odd ordinal numbers form the key array, and parameters with even ordinal numbers form the value array.
- The data element types of key1~keyN and value1~valueN are described in Overview of map data types.
- Note that the keys in the input key-value pairs must be unique. If there are duplicate keys, the later input value will overwrite the earlier one.
The return value is a map data type (MAP).
Here are some examples:
-- Construct a map with one key-value pair, where the key is 1 and the value is 2.
SELECT map(1,2);
+----------+
| map(1,2) |
+----------+
| {1:2} |
+----------+
1 row in set
-- Construct a map with three key-value pairs.
SELECT map(1,"a",2,"b",3,"c");
+------------------------+
| map(1,"a",2,"b",3,"c") |
+------------------------+
| {1:"a",2:"b",3:"c"} |
+------------------------+
1 row in set
-- The data types of the key array and value array are determined by the parameters with odd and even ordinal numbers, respectively.
SELECT map(1,"a","b",1.8,"ccc",3);
+-------------------------------+
| map(1,"a","b",1.8,"ccc",3) |
+-------------------------------+
| {"1":"a","b":"1.8","ccc":"3"} |
+-------------------------------+